[Sync] Split UserEventService into interface and impl, add fake impl, add unit tests.

components/sync/user_events/fake_user_event_service.h

Index: components/sync/user_events/fake_user_event_service.h
diff --git a/components/sync/user_events/fake_user_event_service.h b/components/sync/user_events/fake_user_event_service.h
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index 0000000000000000000000000000000000000000..39399c33710b7946c79a6ea6c5b6d181b45e8477
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+++ b/components/sync/user_events/fake_user_event_service.h
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+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COMPONENTS_SYNC_USER_EVENTS_FAKE_USER_EVENT_SERVICE_H_
+#define COMPONENTS_SYNC_USER_EVENTS_FAKE_USER_EVENT_SERVICE_H_
+
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/memory/weak_ptr.h"
+#include "components/sync/protocol/user_event_specifics.pb.h"
+#include "components/sync/user_events/user_event_service.h"
+
+namespace syncer {
+
+class ModelTypeSyncBridge;
+
+// This implementation is intended to be used in unit tests, with public
+// accessors that allow reading all data to verify expectations.
+class FakeUserEventService : public UserEventService {
+ public:
+  FakeUserEventService();
+  ~FakeUserEventService() override;
+
+  // UserEventService implementation.
+  void RecordUserEvent(
+      std::unique_ptr<sync_pb::UserEventSpecifics> specifics) override;
+  void RecordUserEvent(const sync_pb::UserEventSpecifics& specifics) override;
+  void RegisterDependentFieldTrial(
+      const std::string& trial_name,
+      sync_pb::UserEventSpecifics::EventCase event_case) override;
+  base::WeakPtr<ModelTypeSyncBridge> GetSyncBridge() override;
+
+  const std::vector<sync_pb::UserEventSpecifics>& GetRecordedUserEvents() const;
+  const std::map<std::string, std::set<sync_pb::UserEventSpecifics::EventCase>>&
+  GetRegisteredDependentFieldTrials() const;
+
+ private:
+  std::vector<sync_pb::UserEventSpecifics> recorded_user_events_;
+  std::map<std::string, std::set<sync_pb::UserEventSpecifics::EventCase>>
+      registered_dependent_field_trials_;
+
+  DISALLOW_COPY_AND_ASSIGN(FakeUserEventService);
+};
+
+}  // namespace syncer
+
+#endif  // COMPONENTS_SYNC_USER_EVENTS_FAKE_USER_EVENT_SERVICE_H_